Patients with idiopathic Parkinson’s syndrome (IPS) show dysexecutive deficits which are not related to dementia. We investigated whether these deficits may be caused by a disturbed interaction of prefrontal cortex and selective basal ganglia loops. 5 healthy right-handed volunteers and 5 non demented IPS patients were studied with FDG PET while performing a gambling task paradigm. Control subjects and patients showed consistent bilateral activation of the dorsolateral prefrontal cortex (DLPFC) and the left caudate. Only controls activated the right cingulate, mesial prefrontal and frontoorbital cortex. Patients significantly deactivated the right thalamus. Thus missing frontoorbital and frontomesial activity may indicate an impairment of the basal ganglia loop in IPS, connecting those regions to the thalamus via the ventral striate. The connections between DLPFC and Thalamus via the left caudate remained intact. This impairment may be the neuroanatomical correlate for dysexecutive syndromes in IPS more related to misjudgement than cognitive impairment.